Device and method for performing an emergency braking function

Abstract

Device for performing an emergency braking function in a motor vehicle, comprising, - a pressure regulating valve (PCR), - a switching valve (SV), - at least two inlet valves (LREV, RREV), each of which is assigned to a wheel brake cylinder (RL, RR), - a return pump (sRP2) whose delivery outlet leads to at least two inlet valves (LREV, RREV), to the switching valve (SV), and to the high-pressure side of the pressure regulating valve (PCR), - a brake fluid reservoir (101) whose outlet is connected to the low-pressure side of the pressure regulating valve (PCR) and to the suction inlet of the return pump (sRP2), - a brake booster (103) whose output is connected via the switching valve (SV) to the delivery output of the return pump (sRP2) and the inlet valves (LREV, RREV), - at least two outlet valves (LRAV, RRAV) which are connected to the suction side of the return pump (sRP2) and the brake fluid reservoir (101), wherein each outlet valve is assigned to a wheel brake cylinder (RL, RR), characterized by - a pressure relief valve (100), - a high-pressure accumulator (HPA) whose inlet is connected to the delivery side of the return pump (sRP2) via a non-return valve (NRV) and - whose outlet is connected via the pressure relief valve (100) to the at least two inlet valves (LREV, RREV) and not to the suction side of the return pump (sRP2).

Description

State of the art

[0001] In order to avoid collisions or at least significantly reduce the consequences of an accident, a vehicle dynamics control system must have a high pressure build-up dynamic. Conventional vehicle dynamics control systems use piston pumps to build up pressure, which deliver a volume flow proportional to the pump speed. As the back pressure increases, the maximum engine speed and thus also the maximum volume flow rate decreases due to the available engine torque. The volume absorption of common hydraulic brake systems with a high initial volume to overcome clearance and tolerances and a relatively soft initial range, i.e. there is a low ratio of volume to pressure, leads in this combination to a relatively slow pressure build-up at the beginning. This means that a large change in volume leads to only a small change in pressure.

[0002] From DE 10 2009 001 401 A1 a braking system for a vehicle is known, comprising a master brake cylinder which is coupled to a brake input element in such a way that a brake pressure and / or actuation travel signal can be provided to the master brake cylinder without amplification and a corresponding unamplified pressure signal can be output by the master brake cylinder, a brake circuit with a separating device which can be switched into an open mode and into a closed mode and at least one wheel brake cylinder arranged at an edge, wherein the unamplified pressure signal can be forwarded to the first wheel brake cylinder when the separating device is in an open mode and a forwarding of the unamplified pressure signal can be prevented by the separating device switched into the closed mode, and a hydraulic unit which is coupled to the first wheel brake cylinder and is designed to output a boost pressure signal.

[0003] Another braking system is known from the published patent application DE 198 35 250 A1. Disclosure of the invention

[0004] The invention relates to a device or a hydraulic circuit for carrying out an emergency braking function in a motor vehicle, comprising - a pressure control valve, - a switching valve, - at least two inlet valves, each of the inlet valves being assigned to a wheel brake cylinder, - a return pump, the delivery outlet of which leads to at least two inlet valves, to the switching valve and to the high-pressure side of the pressure control valve, - a brake fluid reservoir whose outlet is connected to the low-pressure side of the pressure control valve and to the suction inlet of the return pump, - a brake booster, the output of which is connected via the switching valve to the delivery output of the return pump and the inlet valves, - and at least two outlet valves which are connected to the suction side of the return pump and the brake fluid reservoir, each outlet valve being assigned to a wheel brake cylinder.

[0005] The essence of the invention is that - a pressure relief valve is included, - and a high-pressure accumulator, the inlet of which is connected to the discharge side of the return pump via a check valve and the outlet of which is connected via the pressure relief valve to the at least two inlet valves and not to the suction side of the return pump.

[0006] This makes it possible to simply charge the high-pressure accumulator via the return pump, as well as to quickly build up brake pressure, thanks to the inventively positioned high-pressure accumulator. The pressure relief valve can be designed, for example, as a switching valve or as a controllable valve.

[0007] An advantageous embodiment of the invention is characterized in that a check valve is arranged between the pressure relief valve and the at least two inlet valves. This prevents brake fluid volume from flowing back into the high-pressure accumulator if the hydraulic pressure in the brake circuit is greater than the pressure in the high-pressure accumulator, thus increasing the volume consumption of the brake system.

[0008] An advantageous embodiment of the invention is characterized in that the outlet of the pressure relief valve is connected to the two inlet valves of only one brake circuit of the motor vehicle.

[0009] An advantageous embodiment of the invention is characterized in that the brake circuit is the brake circuit that brakes the rear wheels of the motor vehicle.

[0010] An advantageous embodiment of the invention is characterized in that the outlet of the pressure relief valve is connected to the inlet valves of both brake circuits of the motor vehicle.

[0011] An advantageous embodiment of the invention is characterized in that, in this case, a check valve for each brake circuit is arranged between the pressure relief valve and the two inlet valves of each brake circuit. This simultaneously prevents pressure equalization between the two brake circuits.

[0012] An advantageous embodiment of the invention is characterized in that a pressure sensor is included which detects the pressure of the brake medium at the delivery outlet of the return pump.

[0013] An advantageous embodiment of the invention is characterized in that the pressure control valve is designed such that it opens when a predetermined pressure difference is reached.

[0014] The last two designs allow for easy adjustment of the target pressure in the high-pressure accumulator by detecting the prevailing pressure with the pressure sensor or by automatically opening the pressure control valve to prevent the target pressure from being exceeded.

[0015] The invention further comprises a method for performing an emergency braking function using a device according to one of the preceding embodiments. The core of the method according to the invention is that the pressure relief valve is opened when an emergency braking request is present.

[0016] The invention further comprises a control unit containing means configured to implement the method according to the invention. The means are, in particular, the program code for the method according to the invention.

[0017] The drawing consists of Fig. 1.

[0018] Fig. Figure 1 shows the hydraulic circuit diagram of a proposed vehicle dynamics control system with rechargeable high-pressure accumulator to reduce the brake pressure build-up time during emergency braking functions.

[0019] The basic idea of ​​the invention is that a pressurized stored volume in the hydraulic circuit can fill at least the initial volume of the brake system, allowing the piston pump to rapidly build up pressure in the stiffer region of the volume-pressure characteristic curve. The term "stiffer region of the volume-pressure characteristic curve" refers to the region of the characteristic curve where a small change in volume leads to a large change in pressure.

[0020] This is intended to significantly reduce the time it takes to reach the locking pressure in the wheel brake cylinders, and thus also the braking distance during an emergency stop. Advantageously, the pressure accumulator can be dimensioned large enough to supply the required brake fluid volume to reach the locking pressure level in the wheel brake cylinders.

[0021] Furthermore, the hydraulic circuit configuration offers the possibility of charging the high-pressure accumulator to its target pressure without an additional pressure sensor. The pressure build-up is carried out via the return pump, and the target pressure is regulated via the pressure-adjustable pressure control valve PCR with the isolation valve SV closed in the left brake circuit of Fig. 1.

[0022] In Fig.Figure 1 shows a hydraulic circuit diagram of a vehicle dynamics control system with a rechargeable high-pressure accumulator (HDS), which reduces the time until locking pressure is reached during emergency braking. The left brake circuit, which controls the wheel brake cylinders RL and RR, is a by-wire brake circuit, while the right brake circuit, which controls the wheel brake cylinders FL and FR, is a coupled brake circuit, as is common in vehicle dynamics control systems. The inlet valves of the wheel brake cylinders are designated LREV, RREV, LFEV, and RFEV; the outlet valves are designated LRAV, RRAV, LFAV, and RFAV. M denotes the electric motor that drives the return pumps sRP2 and sRP1, which are usually designed as piston pumps.

[0023] The return pumps are preferably designed as three-piston pumps, which allows for additional flow into the high-pressure accumulator. However, the use of single-piston pumps is also conceivable. 101 designates the brake fluid reservoir, 103 the brake booster.

[0024] On the pressure side of the by-wire brake circuit, a high-pressure accumulator (HDS) is connected via a check valve (RVR). From this, the pressurized volume from the high-pressure accumulator can be released into both brake circuits via a switchable or, preferably, even adjustable pressure relief valve (100) and an additional check valve (RVR2 and RVR3) in order to actively build up pressure there. The two check valves (RVR2 and RVR3) are designed to prevent brake fluid from flowing back into the high-pressure accumulator at higher circuit pressures, thereby increasing the brake system's volume consumption.

[0025] Initially, the high-pressure accumulator must be charged. To do this, the isolation valve SV is closed, and the piston pump sRP2, with the inlet valves closed, pumps volume from reservoir 101 through the check valve RVR into the high-pressure accumulator. The pressure control valve PCR is used to adjust the pressure in the high-pressure accumulator, setting the target pressure.

[0026] This target pressure can be measured using pressure sensor 104 located in the left brake circuit. Optionally, this pressure sensor can also be omitted for charging the high-pressure accumulator. The pressure control valve can be designed such that it opens automatically due to spring preload at a predetermined pressure difference, e.g., 180 bar. The high-pressure accumulator can then only be charged up to this maximum opening pressure. It is also conceivable to control the return pump only for a predetermined time interval to charge the high-pressure accumulator.

[0027] As soon as automatic emergency braking is requested, in addition to the flow rate that the return pumps of both circuits can deliver, pressurized volume is released from the high-pressure accumulator into both brake circuits by opening or adjusting the pressure relief valve 100. This can support the pressure buildup in both brake circuits until an equilibrium is established between the circuit pressure and the high-pressure accumulator pressure. At this point, the pressure relief valve 100 can then be closed.

[0028] The two check valves RVR2 and RVR3 behind the pressure relief valve prevent brake fluid from flowing back into the high-pressure accumulator when the circuit pressure continues to rise.

Claims

[1] Device for performing an emergency braking function in a motor vehicle, comprising - a pressure control valve (PCR), - a switching valve (SV), - at least two inlet valves (LREV, RREV), each of the inlet valves being assigned to a wheel brake cylinder (RL, RR), - a return pump (sRP2), the delivery outlet of which leads to at least two inlet valves (LREV, RREV), to the switching valve (SV), and to the high-pressure side of the pressure control valve (PCR), - a brake fluid reservoir (101), the outlet of which is connected to the low-pressure side of the pressure control valve (PCR) and to the suction inlet of the return pump (sRP2), - a brake booster (103), the output of which is connected via the switching valve (SV) to the delivery output of the return pump (sRP2) and the inlet valves (LREV, RREV), - at least two outlet valves (LRAV, RRAV) which are connected to the suction side of the return pump (sRP2) and the brake fluid reservoir (101), each outlet valve being assigned to a wheel brake cylinder (RL, RR), characterized by - a pressure relief valve (100), - a high-pressure accumulator (HDS), the inlet of which is connected to the discharge side of the return pump (sRP2) via a check valve (RVR) and - the outlet of which is connected via the pressure relief valve (100) to the at least two inlet valves (LREV, RREV) and not to the suction side of the return pump (sRP2). [2] Device according to claim 1, characterized by that a check valve (RVR2) is arranged between the pressure relief valve (100) and the at least two inlet valves (LREV, RREV). [3] Device according to claim 1, characterized bythat the outlet of the pressure relief valve is connected to the two inlet valves (LREV, RREV) of only one brake circuit of the motor vehicle. [4] Device according to claim 3, characterized by that the brake circuit is the brake circuit that brakes the rear wheels of the motor vehicle. [5] Device according to claim 1, characterized by that the outlet of the pressure relief valve is connected to the inlet valves (LREV, RREV, LFEV, RFEV) of both brake circuits of the vehicle. [6] Device according to claim 1, characterized by that a check valve (RVR2, RVR1) is arranged between the pressure relief valve (100) and the two inlet valves (LREV, RREV) of a brake circuit. [7] Device according to claim 1, characterized by that a pressure sensor (104) is included which detects the pressure of the brake medium at the delivery outlet of the return pump (sRP2). [8] Device according to claim 1, characterized bythat the pressure control valve (PCR) is designed in such a way that it opens when a predetermined pressure difference is reached. [9] Method for carrying out an emergency braking function by means of a device according to one of the preceding claims, characterized by that when an emergency braking request is present, the pressure relief valve (100) is opened. [10] Control device comprising means designed to carry out the method according to claim 7.

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